'81 -'82 maple boards on the concords were different to the '83 onwards, much thinner and a lot less glossy, a damp soapy cloth should clean any maple board, though I do like to use a light dab of acetone on a rag to clean the scum off.

The original finish was likely a thinner version of the urethane used on the body finish. As you've just heard, the thickness and gloss varied form year to year.

I usually find mild soap and water with a toothbrush is enough to remove the fret poo from most maple boards. Don't let the water sit long though, wipe it dry with paper towels then finish off with a good quality wax if needed, and polish to a nice shine.

If the frets need attention be sure to use a fret shield and #0000 steel wool prior to the waxing.